1. Field of the Invention
This invention relates to novel 2-cyano-4-halogenophenyl esters as well as liquid crystal compositions containing the above-mentioned compounds and exhibiting a negative dielectric anisotropy.
2. Description of the Prior Art
Liquid crystal display elements utilize optical anisotropy and dielectric anisotropy of liquid crystal substances, and are classified into various types such as TN (twisted, nematic) type, DS (dynamic scattering) type, guest-host type, DAP type, according to their display modes, and the properties of liquid crystal substances required for their respective uses are different. Anyhow, however, in any mode, liquid crystal substances are necessary to be stable to heat, air, light, etc. and also are desirable to exhibit a liquid crystal phase in temperature ranges as broad as possible, around room temperature. At present, however, no single compound which alone satisfies such conditions is present, and it is the present status that several kinds of liquid crystal compounds or these compounds and compounds which themselves are non-liquid crystalline but, when combined with liquid crystal compounds, can form a liquid crystal composition, have been blended and the resulting liquid crystal compositions have been used.
Recently, guest-host type liquid crystal display elements as a mode of color liquid crystal display method have come to be particularly noted. For the elements, mixtures of liquid crystals and dyestuffs are used, and for positive type guest-host type display elements, liquid crystals having a negative dielectric anisotropy are used. Thus, as the constituents of such liquid crystals, liquid crystal compounds which have various specific properties, a good compatibility and a negative dielectric anisotropy have been required. The present inventors have made studies for obtaining compounds satisfying such requirement.
The object of the present invention is to provide novel compounds which are useful as constituents of liquid crystal compositions exhibiting a negative dielectric anisotropy.